Inorganic materis for anomalous-dispersion phase-matched second harmonic generation: Rubidium titanyl arsenate isomorphs, Rb[Ti{sub 1-2x}Ln{sub x}Nb{sub x}]OAsO{sub 4}

We report the synthesis and optical properties of Rb[Ti{sub 1-2x}Ln{sub x}Nb{sub x}]OAsO{sub 4}. The solid solubility of lanthanide ions in the materials decreases exponentially as the size of the lanthanide ion increases. The materials exhibit absorption spectra characteristic of the particular lanthanide ion in the structure. The spectral regions between absorption peaks are transparent and will allow the transmission of fundamental and second-harmonic radiation. The charge transfer band is red-shifted 0 to 27 nm relative to RbTiOAsO{sub 4} (midpoint 331 nm). Second-harmonic intensities measured at 532 nm decrease exponentially as lanthanide ion concentration increases

Optical And Transport Properties Of An Alkali-doped Methanofullerene

We examine the effects of monoderivatization on the electronic properties of C60. For this we chose the phenyl-C61-octanoic acid cholesteryl ester, [6,6]PCOCr, whose nonlinear optical properties have been investigated in the past. While the optical absorption spectrum of this methano fullerene is similar to that of C60, substantial differences are observed upon doping with potassium. Similarly, the doping-dependent conductivity of the functionalized fullerene shows two maxima as opposed to the single maximum for C60. The experimental observations are consistent with the doping-induced degeneracy removal of the parent C60 LUMO (t1u) orbital, which in potassium-doped methanofullerene splits into two components separated by about 0.5 eV. We provide experimental evidence that the doping of [6,6]PCOCr proceeds, as in C60, with six consecutive reduction (electron transfer) steps, yielding K6[6,6]PCOCr stoichiometry at the end. The transport in partially doped [6,6]PCOCr thin films occurs by thermally activated hopping of the charge carriers with activation energy Ea~=0.25 eV and hopping probability proportional to the number of unpaired electrons in the reduced molecule.

VO2(B) nanorods: solvothermal preparation, electrical properties, and conversion to rutile VO2 and V2O3

The solvothermal reduction of V2O5 by formaldehyde or isopropanol yields nanorods of the metastable, monoclinic VO2(B) phase. The structural transition in VO2(B), which occurs near room temperature, has been monitored using electrical resistivity measurements, performed both on pressed pellets of the nanorods as well as on nanorods dispersed on patterned contacts. A sudden, 105 increase in the electrical resistivity upon cooling below 290 K is seen in measurements on VO2(B) samples. Such a transition in the electrical resistivity has not previously been reported in this material. The transition is reminiscent of the metal-to-insulator transition observed in the case of pressed pellets of polycrystalline rutile VO2 upon cooling below 340 K. The metastable VO2(B) nanorods are converted to rutile VO2 by heating in argon, and to corundum V2O3 by reducing in 5H2 : 95N2. In both transformations, the structural integrity of the nanorods is compromised, with large, dense, rutile VO2 crystallites and less well-defined nanorods of V2O3 being formed

The creation of MOx surface species on pure silica MCM-48, using gas- and liquid phase modification with M-acetylacetonate complexes

Pure silica MCM-48 is prepared by a novel synthesis method, using the [C18H37N+(CH3)(2) - (CH2)(12) - N+(CH3)(2)C18H37].2Br(-) surfactant, abbreviated as GEMINI 18-12-18. The MCM-48, obtained after careful calcination, is a highly crystalline, mesoporous material, with the characteristics of the Ia3d cubic phase, a surface area exceeding 1000 m(2)/g and a narrow mesoporous pore size distribution (r = 1.4 nm; FWHH < 0.2 nm). This MCM support is grafted with VOx species, using a designed dispersion of VO(acac)(2) in a gas deposition reactor. In a first step, the complex is anchored to the support, in a subsequent step the adsorbed complex is thermolyzed to yield chemically bonded VOx surface species. The final material contains 1.7 mmol V/g (8.7 w% V), still has narrow pore size distribution and a surface area of 800 m(2)/g. It is observed that all silanols are consumed during the adsorption of the VO(acac)(2) complex to the MCM support. Therefore, the maximum achievable number of surface V-species is limited by the silanol number, and not by the geometrical surface, which has a higher capacity. After calcination of the adsorbed complex, the supported VOx species are present in a strictly tetrahedral configuration, but mainly as chains of linked tetrahedra and not as isolated species

Understanding the Operating Mechanism of Aqueous Pentyl Viologen/Bromide Redox-Enhanced Electrochemical Capacitors with Ordered Mesoporous Carbon Electrodes

Compared to traditional electric double-layer capacitors, redox-enhanced electrochemical capacitors (redox-ECs) show increased energy density and steadier power output thanks to the use of redox-active electrolytes. The aim of this study is to understand the electrochemical mechanisms of the aqueous pentyl viologen/bromide dual redox system at the interface of an ordered mesoporous carbon (CMK-8) and improve the device performance. Cells with CMK-8 carbon electrodes were investigated in several configurations using different charging rates and potential windows. The pentyl viologen electrochemistry shows a mixed behavior between solution-based diffusion and adsorption phenomena, with the reversible formation of an adsorbed layer. The extension of the voltage window allows for full reduction of the viologen molecules during charge and a consequent increase in the specific discharge energy delivered by the cell. Investigation of the mechanism indicates that a 1.5 V charging voltage with a 0.5 A g-1 charging rate and fast discharge rate produces the best overall performance

Ordered mesoporous metallic MoO2 materials with highly reversible lithium storage capacity

Highly ordered mesoporous crystalline MoO2 materials with bicontinuous Ia3d mesostructure were synthesized by using phosphomolybdic acid as a precursor and mesoporous silica KIT-6 as a hard template in a 10 H2 atmosphere via nanocasting strategy. The prepared mesoporous MoO2 material shows a typical metallic conductivity with a low resistivity, which makes it different from all previously reported mesoporous metal oxides materials. Primary test found that mesoporous MoO2 material exhibits a reversible electrochemical lithium storage capacity as high as 750 mA h g-1 at C/20 after 30 cycles, rendering it as a promising anode material for lithium ion batteries

Large thermoelectric figure of merit at high temperature in Czochralski-grown clathrate Ba8Ga16Ge30

The Czochralski method was used to grow a 46-mm -long crystal of the Ba8 Ga16 Ge30 clathrate, which was cut into disks that were evaluated for thermoelectric performance. The Seebeck coefficient and electrical and thermal conductivities all showed evidence of a transition from extrinsic to intrinsic behavior in the range of 600-900 K. The corresponding figure of merit (ZT) was found to be a record high of 1.35 at 900 K and with an extrapolated maximum of 1.63 at 1100 K. This makes the Ba8 Ga16 Ge30 clathrate an exceptionally strong candidate for medium and high-temperature thermoelectric applications